The invention relates to pipe repair clamps of the type in which rigid lugs are used to bring together the ends of a malleable band that extends around the pipe. More particularly, the invention relates to an improved connection for securing the ends of the band to the lug, and to a method for making the improved connection.
Pipe clamps utilizing a malleable band attached to rigid lugs are now widely used because of their versatility and effectiveness in meeting various conditions. In more recently developed clamps, the problem of bolt bending due to the tendency of the lugs to tip as the bolts are tightened has been largely overcome through the use of low bolt clamps with projecting fingers, and in these improved clamps greater amounts of torque can be applied to draw the lugs together. However, the ability of the lugs to withstand a greater band tightening force has increased the problem of securing the ends of the malleable band to the lugs. Accordingly, a general object of the present invention is to provide an improved pipe clamp structure for connecting the malleable bands to a pair of rigid lugs so that the band cannot possibly slip from the lugs or break loose from them, even when an unusually large tightening force is applied to draw the lugs together.
Efforts have long been made to provide a connecting structure for attaching the lugs to the flexible band that not only had adequate strength but also was practical and inexpensive to manufacture. In U.S. Pat. Nos. 3,089,212, 3,209,427 and 3,584,353 a slotted lug edge was utilized, with the band end crimped between the upper and lower jaws of the slot and deformed by projections on one jaw and corresponding recesses on the other jaw, as a gripping means.
U.S. Pat. No. 3,195,206 disclosed a lug-to-band connection wherein sharp tooth-like elements on the initially open jaws would bite into and grip the malleable band end when the jaws were clamped together onto the band. U.S. Pat. No. 3,254,387 disclosed another gripping means wherein one of the open lug jaws had projections which, upon closure of the jaws, would pass through an opening in the band end to grip the band. Other band gripping means have been disclosed in U.S. Pat. Nos. 3,183,938 and 3,267,547. In some connections the two jaws of the lug have been pinned together through the band in an attempt to prevent later separation of the jaws, but this has proven ineffective.
A pipe clamp made entirely from rolled or extruded metal and welded together is disclosed in U.S. Pat. No. 3,737,959. The lugs of that pipe clamp also gripped the band via a slot in the lug in which the band end was positioned. The three relatively thin layers of metal--the two lug jaws and the band--were then spotwelded at intervals along the lug, binding all three layers together at the weld points. This has been a standard practice in sheet metal work, for securing a sheet metal "sandwich". Although the present invention described below involves welding among a pair of jaws and a band, it is a very different type of weld and welding operation and is particularly advantageous for reasons which will be discussed below.